Enhancing the brightness and increasing the miniaturization of projection display apparatuses leads to a steady increase in the heat densities of optical parts.
Organic optical materials are used for many optical parts of projection display apparatuses, and there is a strong correlation between the operating temperature and deterioration of the display apparatuses. For example, in a liquid crystal type projection display apparatus, a liquid crystal panel, a polarizing plate and an optical compensation plate are used for a liquid crystal panel unit, a polarization beam splitter (PBS) is used for an illumination optical part, and when the temperature of these parts is high, this causes early deterioration of these parts. More specifically, in order to exhibit a desired optical performance and to maintain performance continuously in projection display apparatuses, suppression of temperature rise by cooling means is important.
The cooling means for these optical parts includes a forced-air-cooling type using an air-cooling fan, and a liquid-cooling type using a liquid circulating pump. In order to enhance cooling capacity by using a forced-air-cooling type, the rotational frequency of the fan needs to be increased, and thus noise increases. Further, even if the rotational frequency of the fan is increased, wind velocity does not rise due to wind resistance, and thus improvement in the cooling capacity is limited. Meanwhile, the liquid cooling type has advantages in which the operation noise of the liquid circulating pump is small and the cooling capacity is large, but has the disadvantage in which the operation system, such as piping for liquid circulation, is massive and complicated.
Therefore, many of the projection display apparatuses adopt forced-air-cooling types, and the arts are disclosed in the following Patent Documents 1, 2 and 3.
Patent Document 1 (JP11-295814A) discloses the art of cooling a liquid crystal panel by providing a wind direction plate at a lower portion at the liquid crystal panel side, having a color synthesis prism, and sending forth the wind by a cooling fan in the liquid crystal panel direction. The art has the problem in which the wind direction plate is essential and since installation of the wind direction plate increases wind resistance, the wind velocity is reduced. Further, in a compact projection display apparatus, the liquid crystal panel and the color synthesis prism are close to each other, and therefore, adoption of the art is difficult.
Patent Document 2 (JP2004-61894A) discloses the art of realizing cooling even when the space from a polarizing plate is small by securing a wind passage by providing a cutout portion in the holding frame of a liquid crystal panel. The art has the advantage of not requiring a composition member that is not related to the optical function, such as the wind direction plate disclosed in the above described Patent Document 1, but has the problem in which wind velocity is reduced due increased wind resistance, as in Patent Document 1. Further, the art also has the problem in which the cooling capacity of an analyzer is sacrificed.
The invention disclosed in Patent Document 3 (JP2001-209126A) prevents inclusion of dust into the liquid crystal panel part from outside by encasing the entire liquid crystal panel. In this invention, the liquid crystal panel part is cooled with wind distributed by a first cooling fan, and thereafter, the air after being cooled is heat-exchanged by the wind by a second cooling fan that is provided outside. However, in the projection display apparatuses of recent years, the amount of heat that is generated by the liquid crystal panel parts is large and the heat-exchange efficiency is low, therefore even the temperature of the air in the projection display apparatuses is cooled, the temperature cannot revert to the original temperature (the temperature at the time of starting the display operation). As a result, in the apparatus disclosed in Patent Document 3, circulation of the cooling wind is repeated inside, and therefore, a temperature rise occurs. In order to solve the problem, a large radiator plate and a high-performance second cooling fan need to be provided, but the cost is increased and the entire projection display apparatus increases in size.
In the arts disclosed in the above Patent Documents 1 to 3 and the like, wind is blown from one specific direction to the optical parts, and the direction in which the wind is blown is forcibly change by adding a wind direction plate and as a result of contrivance of the shape to the existing structures.
Therefore, even if further enhancement of the cooling capacity is planned, due to a significant increase in noise, or an increase in wind resistance, enhancement of the cooling capacity is inhibited. Similar problems occur even if the size of the blowout port is reduced in order to enhance the wind velocity at the cooling wind blowout port of the duct.
Further, even if the size of the projecting display apparatus is increased and is mounted with a high performance cooling fan, and even if a rise in wind velocity, which overcomes any increase in wind resistance, is realized, the amount of temperature reduction of the optical parts will gradually decreases with respect to the rising amount of wind velocity, and therefore cooling efficiency will be lowered. In order to avoid this phenomenon and reduce the temperature of the optical parts, it is necessary to enlarge the heat radiation area of the heat generation surface, or raise the heat transfer rate.